In
electrical engineering
Electrical engineering is an engineering discipline concerned with the study, design, and application of equipment, devices, and systems that use electricity, electronics, and electromagnetism. It emerged as an identifiable occupation in the l ...
, a node is any region or joining point on a
circuit between two
circuit elements. In
circuit diagram
A circuit diagram (or: wiring diagram, electrical diagram, elementary diagram, electronic schematic) is a graphical representation of an Electrical network, electrical circuit. A pictorial circuit diagram uses simple images of components, whil ...
s, connections are ideal
wire
file:Sample cross-section of high tension power (pylon) line.jpg, Overhead power cabling. The conductor consists of seven strands of steel (centre, high tensile strength), surrounded by four outer layers of aluminium (high conductivity). Sample d ...
s with zero
resistance. Whether "node" refers to a single point of junction or an entire equipotential region varies by the source.
"Node" is often used, especially in
mesh analysis
Mesh analysis (or the mesh current method) is a circuit analysis method for Planar graph, planar circuits; planar circuits are circuits that can be drawn on a Plane (mathematics), plane surface with no wires crossing each other. A more general ...
, to mean a principal node, which is distinct from the usage defined above. A principal node is a point in a circuit diagram where three or more connections meet. Principal nodes are important points of consideration in applying
Kirchhoff's circuit laws
Kirchhoff's circuit laws are two equalities that deal with the current and potential difference (commonly known as voltage) in the lumped element model of electrical circuits. They were first described in 1845 by German physicist Gustav Kirc ...
, because conservation of current means current can split or combine at these points.
When clarification is needed, a region connecting only two circuit elements is referred to as a simple node, where there is no branching of current, while a point connecting three or more elements is a ''principal node''. The full definition uses in this article encompasses both principal and simple nodes.
Details
According to
Ohm's law
Ohm's law states that the electric current through a Electrical conductor, conductor between two Node (circuits), points is directly Proportionality (mathematics), proportional to the voltage across the two points. Introducing the constant of ...
, , the
voltage
Voltage, also known as (electrical) potential difference, electric pressure, or electric tension, is the difference in electric potential between two points. In a Electrostatics, static electric field, it corresponds to the Work (electrical), ...
across any two points of a node with negligible resistance is
:
showing that the
electric potential
Electric potential (also called the ''electric field potential'', potential drop, the electrostatic potential) is defined as electric potential energy per unit of electric charge. More precisely, electric potential is the amount of work (physic ...
at every point of a node is the same.
There are some notable exceptions where the
voltage difference is large enough to become significant:
* High-precision resistance measurements using a
Kelvin connection
* The difference in voltage between
ground and neutral, between the
neutral wire and the
ground in
domestic AC power plugs and sockets, can be fatal. A properly installed electrical system connects them together at only one location, leading many people to the fatally incorrect conclusion that they are at "the same" voltage, or that the safety ground is "redundant and unnecessary"
* The
Seebeck effect and the
Peltier effect
* Joints involving
aluminium wire
Dots used to mark nodes on a circuit diagram are sometimes referred to as ''meatballs''.
[Mansfield, Michael; O'Sullivan, Colm (2010), ''Understanding Physics (2nd edition)'', Chapter 14, page 359, John Wiley & Sons]
References
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Electricity